In signal transmission systems, such as mobile radio systems, it is necessary for one of the communication partners (first transmission unit) to detect specific fixed signals which are emitted by another communication partner (second transmission unit). These can be, for example, what are termed synchronization bursts for synchronizing two synchronization partners such as radio stations, for example, or what are termed access bursts.
In order to detect or identify such received signals reliably by contrast with the ambient noise, it is known to correlate the received signal continuously with a prescribed signal sequence over a fixed time duration, and to form the correlation sum over the time duration of the prescribed signal sequence. The range of the received signal, which yields a maximum correlation sum, corresponds to the signal being searched for. Connected upstream, as what is termed a training sequence, of the synchronization signal from the base station of a digital mobile radio system, is, for example, a signal sequence which is detected or determined in the mobile station in the way just described by correlation with the stored signal sequence. The mobile stations can, thus, be synchronized with the base station.
Such correlation calculations are also necessary in the base stations; for example, in the case of random-access-channel (RACH) detection. Moreover, a correlation calculation is also carried out to determine the channel pulse response and the signal propagation times of received signal bursts.
The correlation sum is calculated as follows in this case:
  Sm  =            ∑              i        =        0                    n        -        1              ⁢                  ⁢                  E        ⁡                  (                      i            +            m                    )                    *              K        ⁡                  (          i          )                    E(i) being a received signal sequence derived from the received signal, and K(i) being the prescribed signal sequence, i running from 0 to n−1. The correlation sum Sm is calculated sequentially for a number of temporally offset signal sequences E(i) obtained from the received signal, and then maximum value of Sm is determined. If k sequential correlation sums are to be calculated, the outlay on calculation is k*n operations, the multiplication and addition being counted together as one operation.
The calculation of the correlation sums is, therefore, very complicated and, particularly in real time applications such as voice communication or radio telephony or in CDMA systems, requires powerful, and expensive processors which have a high power consumption during calculation. For example, a known signal sequence of length 256 chips (a transmitted bit is also termed a chip in CDMA) is to be determined for the purpose of synchronizing the UMTS mobile radio system, which is being standardized. The sequence is repeated every 2560 chips. Since the mobile station initially operates asynchronously relative to the chip clock, the received signal must be oversampled in order to retain an adequate signal even given an unfavorable sampling situation. Because of the sampling of the I and Q components, this leads to 256*2560*2*2=2621440 operations.
WO 96 39749 A discloses transmitting a synchronization sequence, a chip of the sequence itself being a sequence.
The use of Golay sequences as an alternative to PN sequences is known from “Srdjan Budisin: Golay Complementary Sequences are Superior to PN Sequences, Proceedings of the International Conference on Systems Engineering, U.S., New York, IEEE, Vol.-, 1992, pages 101–104, XP 000319401 ISBN: 0-7803-0734-8”.
It is an object of the present invention to specify methods for synchronizing a base station with a mobile station, as well as to specify a base station and a mobile station, which permits a base station to be synchronized with a mobile station in a way which is reliable and favorable in terms of outlay.